Electrolytically polished graphite anode



Patented Jan. 10, 1950 ELECTROLYTICALLY POLISHED GRAPHITE AN ODE Jan Bakker, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn, as trustee No Drawing. Application July 2, 1946, Serial No. 681,124. In the Netherlands March 15, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires March 15, 1963 2 Claims.

This invention relates to a gasand/or vapourfilled current-converting tube Whose anode is of graphite.

Graphite has been used fora long time as material for anodes in gas or vapour-filled current-converting tubes. It has a lot of good properties, such as high load capacity on account of the low specific emission, even at very high temperatures, low volatilisation and a high coefficient of radiation so that the anode leads need conduct away less heat by conduction. In addition, graphite anodes are materially less liable to arcing back than metal anodes, because of glow discharge on a graphite surface as the cathode does not readily pass into an arc.

Nevertheless, in spite of the good properties of graphite it was frequently difficult to render the anodes of a current-converting tube free from arcing-back under all conditions. The back discharges which occur at any frequency. are put down by divers testers to gas-enclosures in the graphite, impurities in the surface of the anode, for example pieces of ashes or metal mercury or activating material that may condense on the anodes after having found its way from the cathode to the anodes.

According to the invention, gas and/or vapour filled current-converting tubes comprise anodically polished graphite anodes. Anodically polished graphite is as smooth as a mirror and is devoid of grinding or polishing scratches. Anodically polished surfaces may exhibit certain undulations due to irregularities in the starting material but they only become manifest as a certain moir on the surface. It has been found by the applicant that anodically polished anode surfaces are by far less liable to arcing back than coarse surfaces. Probably, there are on an anodically polished surface fewer impurities capable of bringing about arcing back and new impurities do not readily adhere to the surface.

Especially suitable electrolytes for anodically polishing graphite are molten fluorides. The current density is preferably chosen to range between 0.1 and 1 a./cm. and the duration between 1 minute and 1 hour.

In order that the invention may be clearly understood and readily carried into effect it will 2 now be described more fully with reference to the following example.

A graphite cylinder having a length of 8 cms. and a diameter of 2 cms. is arranged as the anode in an electrolysis bath of molten potassium hydrofiuoride KI-IFz which is not entirely anhydrous. At a voltage of volts the anode is loaded for half an hour with a current of 15 amperes. The graphite anode is then as smooth as a mirror. If the graphite rod is housed in a current-converting tube to form the anode and is deprived of gases in the usual manner, the current-converting tube is free from arcing back to a high extent.

What I claim is:

1. An ion discharge tube comprising an electrolytically polished graphite anode.

2. A method of polishing graphite anodes for ion discharge tubes which comprises the steps of positioning the graphite anode as an anode of an electrolytic bath consistin of molten potassium hydrofiuoride KHFz, applying a potential of approximately 130 volts to the said anode, and loading the said anode with a current density of between about 0.1 and 1 a./cm. for about 1 minute to 1 hour.

JAN BAKKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,484,733 Mathers Feb. 26, 1924 1,866,969 Fredenhagen July 12, 1932 2,329,317 Atlee Sept. 14, 1943 FOREIGN PATENTS Number Country Date 401,471 Great Britain Nov. 16, 1933 455,256 Great Britain Oct. 16, 1936 OTHER REFERENCES The Electrochemical Society, Preprint 91-3 (1947), Electrolytic Fluorine Production In Germany, by Neumark; pages 37 through 44. (Copy in Division 56.) 

1. AN ION DISCHARGE TUBE COMPRISING AN ELECTROLYTICALLY POLISHED GRAPHITE ANODE. 